several updates for the stable D8 APIs, almost working state. You can choose fields, you can submit the trimmed node form. What's left: get rid of all deprecated calls, theme the iframe-inside pages, make redirection after node submission, fix menu link

various wording improvements, added link to the result page, user can open nodes right from result page, in new window

display a warning message for non-JS enabled browsers to let the user know why the form does not work

code beauty according to coder module, do not discard the standard drupal messages inside the iframe

remove unneeded lines: session_write_close() is handled by drupal core via register_shutdown_function(), set_breadcrumb() is not needed cause we use html.tpl.php, not the full blown page template

#1761808 reported by arrrgh : handle the situation when there are no fields for some reason, notice(s) appeared

made the global 'Create' button work, added CSS to align fields side-by-side, simplify the code, use html.tpl.php to generate bare page, it does not make sense to use custom html skeleton